A composition containing an alkali-soluble resin and a naphthoquinonediazide compound as a light-sensitive material is generally used as a positive type photoresist composition. For example, a "novolak type phenol resin/naphthoquinonediazide-substituted compound" is described in U.S. Pat. Nos. 3,666,473, 4,115,128 and 4,173,470, and a "novolak resin comprising cresol and formaldehyde/trihydroxybenzophenone-1,1-naphthoquinonediazido-sulfonic acid ester", which is the most typical example, is described in L.F. Thompson, Introduction to Microlithography, ACS Publication Corp., No. 219, pp. 112-121.
Further, triphenylmethane-based light-sensitive material is known as is described in U.S. Pat. No. 3,188,210 and JP-A-60-121445 (The term "JP-A" as used herein means an "unexamined published Japanese patent application").
A novolak resin as a binder is particularly useful in that it is soluble in an aqueous alkali solution without swelling, and when the formed image is used as an etching mask, it provides high durability, particularly against plasma etching. The naphthoquinonediazide compound to be used as a light-sensitive material is specific in that although the naphthoquinonediazide compound itself acts as a dissolution inhibitor to decrease the alkali solubility of the novolak resin, when decomposed by irradiation with light, it produces an alkali-soluble substance and actually serves to increase the alkali solubility of the novolak resin. Because of these changes in properties by irradiatioin with light, the naphthoquinonediazide compound is particularly useful as a light-sensitive material for a positive type photoresist.
In these circumstances, a number of positive type photoresists containing a novolak resin and a naphthoquinonediazide-based light-sensitive material have been developed and put into practical use. They are sufficiently satisfactory for fabrication of line widths up to about 1.5 to 2 .mu.m.
With an increase in the degree of integration for integrated circuits, fabrication of a super fine pattern comprising lines having a width of 1 .mu.m or less is needed in the production of semiconductor substrates, e.g., super LSI. In such applications, a high sensitivity photoresist is needed in terms of high resolving power, high pattern reproduction accuracy to accurately reproduce the form of a light exposure mask, and high productivity. The conventional positive type photoresist, however, fails to meet the above requirements.